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The relative contributions of radial and laminar optic flow to the perception of linear self-motion
(2012)
When illusory self-motion is induced in a stationary observer by optic flow, the perceived distance traveled is generally overestimated relative to the distance of a remembered target (Redlick, Harris, & Jenkin, 2001): subjects feel they have gone further than the simulated distance and indicate that they have arrived at a target's previously seen location too early. In this article we assess how the radial and laminar components of translational optic flow contribute to the perceived distance traveled. Subjects monocularly viewed a target presented in a virtual hallway wallpapered with stripes that periodically changed color to prevent tracking. The target was then extinguished and the visible area of the hallway shrunk to an oval region 40° (h) × 24° (v). Subjects either continued to look centrally or shifted their gaze eccentrically, thus varying the relative amounts of radial and laminar flow visible. They were then presented with visual motion compatible with moving down the hallway toward the target and pressed a button when they perceived that they had reached the target's remembered position. Data were modeled by the output of a leaky spatial integrator (Lappe, Jenkin, & Harris, 2007). The sensory gain varied systematically with viewing eccentricity while the leak constant was independent of viewing eccentricity. Results were modeled as the linear sum of separate mechanisms sensitive to radial and laminar optic flow. Results are compatible with independent channels for processing the radial and laminar flow components of optic flow that add linearly to produce large but predictable errors in perceived distance traveled.
Interactive Distributed Rendering of 3D Scenes on Multiple Xbox 360 Systems and Personal Computers
(2012)
For the case when the abstraction of instantaneous state transitions is adopted, this paper proposes to start fault detection and isolation in an engineering system from a single time-invariant causality bond graph representation of a hybrid model. To that end, the paper picks up on a long-known proposal to model switching devices by a transformer modulated by a Boolean variable and a resistor in fixed conductance causality accounting for its ON resistance. Bond graph representations of hybrid system models developed in this way have been used so far mainly for the purpose of simulation. The paper shows that they can well constitute an approach to the bond-graph-based quantitative fault detection and isolation of hybrid models. Advantages are that the standard sequential causality assignment procedure can be a used without modification. A single set of analytical redundancy relations valid for all physically feasible system modes can be (automatically) derived from the bond graph. Stiff model equations due to small values of the ON resistance in the switch model may be avoided by symbolic reformulation of equations and letting the ON resistance of some switches tend to zero, turning them into ideal switches.
First, for two examples considered in the literature, it is shown that the approach proposed in this paper can produce the same analytical redundancy relations as were obtained from a hybrid bond graph with controlled junctions and the use of a sequential causality assignment procedure especially for fault detection and isolation purpose. Moreover, the usefulness of the proposed approach is illustrated in two case studies by its application to standard switching circuits extensively used in power electronic systems and by simulation of some fault scenarios. The approach, however, is not confined to the fault detection and isolation of such systems. Analytically validated simulation results obtained by means of the program Scilab give confidence in the approach.
A bond graph representation of switching devices known for a long time has been a modulated transformer with a modulus b(t)∈{0,1}∀t≥0 in conjunction with a resistor R:Ron accounting for the ON-resistance of a switch considered non-ideal. Besides other representations, this simple model has been used in bond graphs for simulation of the dynamic behaviour of hybrid systems. A previous article of the author has proposed to use the transformer–resistor pair in bond graphs for fault diagnosis in hybrid systems. Advantages are a unique bond graph for all system modes, the application of the unmodified standard Sequential Causality Assignment Procedure, fixed computational causalities and the derivation of analytical redundancy relations incorporating ‘Boolean’ transformer moduli so that they hold for all system modes. Switches temporarily connect and disconnect model parts. As a result, some independent storage elements may temporarily become dependent, so that the number of state variables is not time-invariant. This article addresses this problem in the context of modelling and simulation of fault scenarios in hybrid systems. In order to keep time-invariant preferred integral causality at storage ports, residual sinks previously introduced by the author are used. When two storage elements become dependent at a switching time instance ts, a residual sink is activated. It enforces that the outputs of two dependent storage elements become immediately equal by imposing the conjugate3 power variable of appropriate value on their inputs. The approach is illustrated by the bond graph modelling and simulation of some fault scenarios in a standard three-phase switched power inverter supplying power into an RL-load in a delta configuration. A well-developed approach to model-based fault detection and isolation is to evaluate the residual of analytical redundancy relations. In this article, analytical redundancy relation residuals have been computed numerically by coupling a bond graph of the faulty system to one of the non-faulty systems by means of residual sinks. The presented approach is not confined to power electronic systems but can be used for hybrid systems in other domains as well. In further work, the RL-load may be replaced by a bond graph model of an alternating current motor in order to study the effect of switch failures in the power inverter on to the dynamic behaviour of the motor.
Ein SLA (Service Level Agreement) legt alle Punkte einer vertraglichen Zusammenarbeit zwischen Unternehmen und Service Provider verbindlich fest. Ein SLA muss sorgfältig erstellt werden, um ein Vertrauensverhältnis zwischen beiden Seiten herzustellen. Dabei geht es um inhaltliche, organisatorische und technische Anforderungen sowie um eine exakte Festlegung auf verwendete Fachbegriffe und Leistungskriterien. Der vorliegende Beitrag beschreibt Punkt für Punkt den Inhalt eines SLA. Das sind u.a. die Benennung der Vetragspartner, die Leistungskriterien, die die Qualität des Dienstes sicherstellen sowie die Überwachung der Erbringung der vereinbarten Leistung und die Dauer des Vertrages.
We present the extensible post processing framework GrIP, usable for experimenting with screen space-based graphics algorithms in arbitrary applications. The user can easily implement new ideas as well as add known operators as components to existing ones. Through a well-defined interface, operators are realized as plugins that are loaded at run-time. Operators can be combined by defining a post processing graph (PPG) using a specific XML-format where nodes are the operators and edges define their dependencies. User-modifiable parameters can be manipulated through an automatically generated GUI. In this paper we describe our approach, show some example effects and give performance numbers for some of them.
We present a graph-based framework for post processing filters, called GrIP, providing the possibility of arranging and connecting compatible filters in a directed, acyclic graph for realtime image manipulation. This means that the construction of whole filter graphs is possible through an external interface, avoiding the necessity of a recompilation cycle after changes in post processing. Filter graphs are implemented as XML files containing a collection of filter nodes with their parameters as well as linkage (dependency) information. Implemented methods include (but are not restricted to) depth of field, depth darkening and an implementation of screen space shadows, all applicable in real-time, with manipulable parameterizations.
In dieser Arbeit wird eine Methode zur Darstellung und Generierung von natürlich wirkendem Bewuchs auf besonders großen Arealen und unter Berücksichtigung ökologischer Faktoren vorgestellt. Die Generierung und Visualisierung von Bewuchs ist aufgrund der Komplexität biologischer Systeme und des Detailreichtums von Pflanzenmodellen ein herausforderndes Gebiet der Computergrafik und ermöglicht es, den Realismus von Landschaftsvisualisierungen erheblich zu steigern. Aufbauend auf [DMS06] wird bei Silva der Bewuchs so generiert, dass die zur Darstellung benötigten Wang-Kacheln und die mit ihnen assoziierten Teilverteilungen wiederverwendet werden können. Dazu wird ein Verfahren vorgestellt, um Poisson Disk Verteilungen mit variablen Radien auf nahtlosen Wang-Kachelmengen ohne rechenintensive globale Optimierung zu erzeugen. Durch die Einbeziehung von Nachbarschaften und frei konfigurierbaren Generierungspipelines können beliebige abiotische und biotische Faktoren bei der Bewuchsgenerierung berücksichtigt werden. Die durch Silva auf Wang-Kacheln erzeugten Pflanzenverteilungen ermöglichen, die darauf aufgebauten beschleunigenden Datenstrukturen bei der Visualisierung wieder zu verwenden. Durch Multi-Level Instancing und eine Schachtelung von Kd-Bäumen ist eine Visualisierung von großen bewachsenen Arealen mit geringen Renderzeiten und geringem Memoryfootprint von Hunderten Quadratkilometern Größe möglich.
In diesem Beitrag wird der interaktive Volumenrenderer Volt für die NVIDIA CUDA Architektur vorgestellt. Die Beschleunigung wird durch das Ausnutzen der technischen Eigenschaften des CUDA Device, durch die Partitionierung des Algorithmus und durch die asynchrone Ausführung des CUDA Kernels erreicht. Parallelität wird auf dem Host, auf dem Device und zwischen Host und Device genutzt. Es wird dargestellt, wie die Berechnungen durch den gezielten Einsatz der Ressourcen effizient durchgeführt werden. Die Ergebnisse werden zurückkopiert, so dass der Kernel nicht auf dem zur Anzeige bestimmten Device ausgeführt werden muss. Synchronisation der CUDA Threads ist nicht notwendig.
This contribution describes an optical laser-based user interaction system designed for virtual reality (VR) environments. The project's objective is to realize a 6-DoF user input device for interaction with VR applications running in CAVE-type visualization environments with flat projections walls. In case of a back-projection VR system, in contrast to optical tracking systems, no camera has to be placed within the visualization environment. Instead, cameras observe patterns of laser beam projections from behind the screens. These patterns are emitted by a hand-held input device. The system is robust with respect to partial occlusion of the laser pattern. An inertial measurement unit is integrated into the device in order to improve robustness and precision.